1. Field of the Invention
The present invention relates to an infrared (IR) absorbing polyvinyl butyral composition, a sheet made therefrom and glass laminates containing the sheet as an interlayer. In particular, the polyvinyl butyral composition contains at least lanthanum hexaboride (LaB6) and more preferably both lanthanum hexaboride and at least one of indium tin oxide (ITO) and antimony tin oxide (ATO).
2. Related Background Art
Polyvinyl butyral (PVB) resin sheet is used in light-transmitting laminates containing one or more rigid layers, such as glass, for applications such as automotive and architectural glazings, show cases, and protective glass for pictures, documents and the like. The PVB sheet absorbs energy and prevents disintegration when, for example, the head of a vehicle occupant strikes the rigid layer of a laminated window after a sudden stop or a foreign object is propelled against the outside of the laminate.
Glazings, including laminated glazings, tend to transmit heat energy. This can be particularly problematic in a confined area, such a vehicle passenger compartment or office, because of potential overheating of the confined area. Thus many techniques have been developed in an attempt to control heat transmission through glazings.
A conventional heat shielding transparent composite may comprise a very thin layer of reflective metal such as aluminum or silver which is deposited on a transparent substrate by vacuum deposition or sputtering techniques. This technique is limited on vehicle and building windows because the film thickness must be extremely thin. In addition, metallic layers may also suffer from corrosion problems.
It is known that nanoparticles of various inorganic oxides, can be dispersed within a resin binder to form coatings that reflect particular wavelength bands of infrared energy and allow high levels of transmission of visible light. In particular, U.S. Pat. No. 5,807,511 discloses that antimony doped tin oxide (ATO) has a very low transmission to infrared light having wavelength exceeding 1400 nm. U.S. Pat. No. 5,518,810 describes coatings containing tin doped indium oxide (ITO) particles that substantially block infrared light having wavelength above 1000 nm, and that the crystal structure of ITO can be modified to block light having wavelengths of down to 700-900 nm.
U.S. Pat. No. 5,830,568 describes a laminated glass with an interlayer film containing functional ultra-fine particles that provide heat insulation, ultraviolet ray absorption or maintenance of sufficient radio transmittance. The preferred interlayer film is polyvinyl butyral or ethylene-vinyl acetate copolymer. The exemplified ultra-fine particles include antimony tin oxide and indium tin oxide.
EP-A-1008564 discloses the use of an infrared blocking coating composition which contains both ATO or ITO, and metal hexaboride such as LaB6. The ATO or ITO blocks the higher wavelengths of infrared light and the metal hexaboride particles block the lower wavelengths of light. The coating may be applied to polymeric film substrates. There is no disclosure or suggestion, however, of employing metal hexaboride as a nanoparticulate dispersion in a PVB composition, particularly for use as an interlayer sheet in a glass laminate.
This invention is directed to a polyvinyl butyral composition comprising polyvinyl butyral resin containing an IR absorbing effective amount of lanthanum hexaboride. Preferably the polyvinyl butyral resin contains an IR absorbing effective amount of a mixture of lanthanum hexaboride and at least one of indium tin oxide and antimony tin oxide. The lanthanum hexaboride and any indium tin oxide and/or antimony tin oxide are present as fine particles, i.e., having a particle size that will not interfere with the visual transmission through a sheet comprised of such an IR absorbing polyvinyl butyral.
This invention is also directed to a sheet formed from the polyvinyl butyral composition of this invention as well as a glass laminate comprised of two sheets of glass having the sheet of this invention disposed therebetween. The sheet formed from the polyvinyl butyral composition of this invention may be used with heat absorbing glass to form a laminate with optimum solar absorbing properties. The glass laminate of this invention is particularly efficient at reducing IR transmission without degradation of the efficiency over time.